Ethylene/α-olefin random copolymers such as EPDM and the like generally have excellent weathering resistance, heat resistance and ozone resistance, and used for electrical wire-covering materials such as electric power cables, cabtyre cords, electric wires for ships, electric insulating rubber tapes, rubber-mold stress cones, electric joint parts and the like, home electric insulating parts such as anode caps, wedges and the like, electric insulating parts for automobiles such as plug caps, grommets, ignition cables, lamp socket covers and the like, terminal covers and semiconductor rubber parts.
Conventional ethylene/α-olefin random copolymers have a defect such that it is inferior in resistance to compression set as compared with silicon rubber etc. To cope with this defect, a method of peroxide cross-linking is more effective than that of sulfur vulcanization. This method, however, has defects that when hot air cross-linking with HAV (hot air vulcanization vessel), UHF (ultra high frequency electromagnetic wave), etc is employed, the surface of a rubber is not cross-linked, or degradation is induced and thereby the scratch resistance of the rubber is extremely deteriorated. The defects are due to the reason that peroxide does not participate in cross-linking and the rubber surface contacts oxygen and thereby degradation proceeds. When the cross-linking is conducted by steam cross-linking with shutting oxygen off or by lead covering cross-linking, the scratch resistance of the rubber surface is improved but the production cost is disadvantageous.
JP-A-H04-154855 discloses a process for preparing a hot air cross-linkable rubber having excellent scratch resistance by using, in a HAV, a rubber composition which comprises a hot air cross-linkable ethylene/propylene/diene copolymer rubber, organohydrodiene polysiloxane having at least two hydrogen atoms bonded with a silicon atom in a molecule, and a platinum catalyst.
However, on testing the invention disclosed in this publication, the present inventors found that the scratch resistance and the resistance to compression set were not sufficiently satisfactory for them.
JP-A-H07-33924 discloses a process for preparing a hot air cross-linkable rubber having excellent scratch resistance by peroxide cross-linking a rubber composition, which is obtainable by adding polysiloxane having at least one reactive group to an ethylene/propylene/diene copolymer rubber.
However, on testing the invention disclosed in this publication, the present inventors found that the cross-linking efficiency is enhanced due to adding of peroxide to the rubber composition, but the scratch resistance of the surface of a rubber molded article after cross-linking is not suitable for practical use because peroxide radicals cause addition reaction of siloxane and also generation of polymer radicals.
Further, JP-A-2001-31808 discloses a polyene-containing copolymer capable of being modified with SiH group. In the polyene containing a vinyl group capable of being modified with SiH group, most of the vinyl groups are used for forming a long chain branch and a part of vinyl groups is only used for the reaction with SiH group so that the efficiency is low. Additionally, the generation of long chain branches causes a lowering of the rubber strength.
Accordingly, the advent of an olefin copolymer having a high cross-linking rate, excellent productivity and capable of preparing molded articles having excellent resistance to compression set, electric properties, strength and other properties, a preparation process thereof and a cross-linkable rubber composition of the copolymer has been desired.
The present invention is intended to solve the problems associated with the prior art as mentioned above, and it is an object of the present invention to provide an olefin copolymer having a high cross-linking rate, excellent productivity and capable of preparing molded articles having excellent resistance to compression set, electric properties, strength and other properties. It is another object of the present invention to provide a cross-linkable rubber composition of the copolymer. It is a further object of the present invention to provide uses thereof including sealing materials, potting materials, coating materials, adhesives and the like.